1. Field of Application
The present invention relates to a cruise control apparatus having a vehicle separation control function, for enabling a controlled vehicle (referred to herein as the “host vehicle”) to follow a preceding vehicle. The invention further relates to a cruise control apparatus having a fixed-speed control function whereby the host vehicle can be controlled to run at a fixed speed as determined by a presettable speed value, and to an adaptive cruise control apparatus incorporating both of these control functions.
2. Description of Prior Art
In the prior art, types of vehicle separation control apparatus are known which are intended to increasing driving safety and decrease the burden on the vehicle driver. With such a vehicle separation control apparatus, the host vehicle can automatically follow a specific preceding vehicle, within a fixed range of vehicle speeds. Another type of vehicle control apparatus is known whereby a driver can set a desired speed value, within a predetermined range, with the host vehicle being controlled to run at that speed. In addition, an adaptive type of cruise control system is known whereby, when cruise control operation has been selected by the driver, the system automatically selects the appropriate mode. That is to say, when the system detects that there is a preceding vehicle, the host vehicle is controlled to follow the preceding vehicle with a specific separation distance, which may be determined in accordance with the vehicle speed, while if no preceding vehicle is located, or if the preceding vehicle cannot be followed, then the host vehicle is controlled to run at a fixed speed which can be preset by the driver. In the following, unless otherwise indicated, the term “cruise control apparatus” is to be understood as referring to an apparatus which implements such a type of adaptive cruise control.
The term “preceding vehicle (of a host vehicle)” as used in the following description and in the appended claims is to be understood as signifying a vehicle which is located on the travel path of the host vehicle, ahead of the host vehicle, with no intervening vehicle, and which meets predetermined conditions of distance and speed in relation to the host vehicle.
With such a cruise control apparatus, external objects which are located ahead of the host vehicle are detected by radar, and a preceding vehicle (if any) is selected from among those detected objects which are estimated to be vehicles. The cruise control apparatus then applies acceleration and deceleration control in accordance with the inter-vehicle distance and relative speeds of the preceding vehicle and host vehicle, such as to maintain as specific separation distance. However, depending upon the environment of the host vehicle, its running condition etc., it is possible that a preceding vehicle may not be correctly recognized. Specifically, it is possible that an object such as a guard rail or signboard, etc., may be detected and erroneously recognized as a vehicle.
In selecting a vehicle as being a preceding vehicle (as defined above), the value of the probability factor that the preceding vehicle is in the same lane as the host vehicle, the time at which the object was detected, etc., may be used as judgement parameters used in the selection process. However, errors in selecting a detected object as being a preceding vehicle do occur, in practical operation.
If the conditions for selecting a preceding vehicle are made too severe, in order to lower the occurrence of detection errors, then this may result in failure to detect some vehicles, i.e., a preceding vehicle may not be correctly selected from among one or more detected objects. It can thus be understood that it is difficult to perform reliable object recognition processing to detect a preceding vehicle, if such processing is based only upon analysis of radar detection data.
That is to say, in the prior art it has been necessary to:    (a) balance the danger of failure to recognize an object which could be a preceding vehicle against the danger of erroneous recognition (e.g., erroneously judging that reflected light from part of a road surface is from an object which could be a vehicle), and    (b) balance the danger of failure to correctly select one of a set of one or more detected objects as being a preceding vehicle (which could result in a collision), against the danger of erroneously selecting an object as being a preceding vehicle (which may result in the host vehicle being controlled to run at an excessively low speed).